1. Field of the Invention
The present invention relates to a printer printing an image corresponding to print data output from a computer.
2. Description of the Related Art
Conventionally, there is a printer, which is provided with an image buffer stored with print data output from a computer, and prints data by transferring the print data stored in this image buffer to a print mechanism in sequence.
FIG. 12 shows a control circuit in such a conventional printer. As shown in FIG. 12, the control circuit in the conventional printer is provided with a communication interface 20, a MPU (micro processing unit) 21, an image buffer 22, a VIF (video interface) 23, an image processing circuit 24, and a print mechanism 25, each connected to one another through a control bus B1. Further, the communication interface 20, the MPU 21, the image buffer 22 and the VIF 23 are connected to one another through a data bus B2.
The MPU 21 is a processing unit controlling an action of each circuit block through the control bus B1.
The communication interface 20 receives the print data transmitted from a host computer (not shown), and transmits the print data to the data bus B2. This print data is transmitted from the computer (or server), and includes character codes, image dot data, printer setting data, commands and the like.
The image buffer 22 is a memory temporarily storing the print data individually transmitted to the data bus B2 from the communication interface 20 in accordance with the control of the MPU 21.
The VIF 23 reads one piece of print data stored in the image buffer 22, and outputs the print data read to the image processing circuit 24 as an image signal which is data from the printer, namely, a video signal, in accordance with the control of the MPU 21. The VIF 23 receives a synchronous signal from the print mechanism 25 when outputting the image signal to the image processing circuit 24, and outputs the image signal in synchronism with this synchronous signal. Further, when the VIF 23 reads a new piece of print data, it is necessary for the MPU 21 to set an address and so on concerning the print data to be read in the image buffer 22.
The image processing circuit 24 applies various image processes set by the MPU 21 to the image signal output from the VIF 23, and then outputs the image signal to the print mechanism 25.
The print mechanism 25, based on the image signal received from the image processing circuit 24, prints an image corresponding to this image signal. The print mechanism 25 gives the synchronous signal to the VIF 23.
As described above, the control circuit in the conventional printer is provided with only one set of the VIF 23 and the image processing circuit 24. Therefore, there are three problems as follows.
The first problem in the conventional printer is explained. Since the control circuit in the conventional printer is provided with only one VIF 23, only an image corresponding to one piece of print data can be printed concerning one page. For example, to print text (data) in a prescribed form, when print data corresponding to the text and print data corresponding to the prescribed form are transmitted from the host computer, the MPU 21 previously integrates two pieces of print data into one piece of print data with a software process, and then stores it in the image buffer 22. In this way, the VIF 23 is capable of printing the text (data) on the prescribed form only by reading one piece of integrated print data from the image buffer 22. However, there is a problem in that the printer operates slowly because the integration process of print data gives a big load to the MPU 21.
The second problem in the conventional printer is explained. Since the control circuit in the conventional printer is provided with only one VIF 23, this VIF 23 must read all of the print data. For example, in a case of a printer having a buffer memory of which capacity is smaller than one page and performing band printing, the VIF 23 must read all bands of print data in sequence transmitted from the host computer. Then, the VIF 23 must be reset by the MPU 21 in order to read a new piece of band print data. During the resetting, the VIF 23 must stop. Accordingly, there is a problem in that the image printed by the print mechanism 25 breaks off when a time necessary to reset the VIF 23 exceeds an allowed time (a time necessary to output all picture signals in a buffer in the VIF 23).
The third problem in the conventional printer is explained. Since the control circuit in the conventional printer is provided with only one image processing circuit 24, one kind of image process concerning one page is able to be executed. However, in a case in which the print data includes text data and image data, it is desirable that an image processing suitable to the text data be applied to the text data while it is desirable that an image processing suitable to image data be applied to the image data. For example, it is desirable to apply the smoothing process to the text data while it is desirable to apply the intermediate tone process to the image data. Further, concerning the resolution of the image, in order to execute high-speed printing, it is desirable to apply the low-resolution process to the text data, while it is desirable to apply the high resolution process to the image data. Moreover, concerning data compression/decompression, it is desirable that, as to the text data, the run-length compression is executed in the host computer and then the run-length decompression is executed in the image processing circuit 24, while it is desirable that, as to the image data, the LZ compression is executed in the host computer and then the LZ decompression is executed in the image processing circuit 24. In spite of such a request for the control circuit in the conventional printer, there is a problem in that only one image process suitable to text data or image data is applied to the print data since there is only one image processing circuit 24.